Generally, a light emitting diode (LED) includes a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode can be formed by combining group III-V elements of the periodic table. The light emitting device can represent various colors by adjusting the compositional ratio of compound semiconductors.
When a forward voltage is applied to an LED, electrons of an N layer are combined with holes of a P layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be released. This energy is mainly realized as heat or light, and the LED emits the energy as the light.
A nitride semiconductor represents superior thermal stability and wide band gap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been commercialized and extensively used.
An ultraviolet light emitting device (UV LED) is a light emitting device of emitting light having the wavelength in the range of 200 nm to 400 nm. The ultraviolet light emitting device includes a short wavelength and a long wavelength depending on the usage thereof. The short wavelength may be used for sterilization or purification and the long wavelength may be used in an exposing device and a curing device.
Meanwhile, the ultraviolet light emitting device may have a problem in which light extraction efficiency may be degraded due to the total reflection on the interfacial surface between the buffer layer and a sapphire substrate. In order to improve the light extraction efficiency, the attempts have been made to form air voids. However, the control of the air voids is difficult.